Synthesis of m13 clusters from aluminum and gallium mineral polymorphs

ABSTRACT

A method comprising reacting an aluminum mineral polymorph or a gallium mineral polymorph with an acid at an aluminum metal to acid molar ratio or gallium metal to acid molar ratio sufficient to produce M13 nanoscale clusters, M nano-agglomerates, or a M13 slurry, wherein M is Al or Ga.

This application is a continuation of U.S. application Ser. No.15/742,412, filed on Jan. 5, 2018, which is the U.S. National Stage ofInternational Application No. PCT/US2016/041622, filed Jul. 8, 2016,which was published in English under PCT Article 21 (2), which in turnclaims the benefit of U.S. Provisional Application No. 62/190,676, filedJul. 9, 2015, which is incorporated herein by reference.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant NumberCHE1102637 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND

Metal oxide (WOO semiconducting materials have had a profound impact onthe market for thin film device applications for numerous years.However, cost-effective mass production of high-purity materials remainschallenging for scientists and engineers.

SUMMARY

Disclosed herein is a method comprising:

reacting an aluminum mineral polymorph or a gallium mineral polymorphwith an acid at an aluminum metal to acid molar ratio or gallium metalto acid molar ratio sufficient to produce M₁₃ nanoscale clusters, Mnano-agglomerates, or a M₁₃ slurry, wherein M is Al or Ga.

Also disclosed herein is a method comprising:

mixing an aluminum mineral polymorph or a gallium mineral polymorph withan acid to produce a slurry; and

processing the slurry under conditions sufficient to produce an aqueoussolution of M₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅ nanoscale clusters,wherein M is Al or Ga.

The foregoing will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural representation of various aluminum materials thatwere converted to flat-Al₁₃ clusters via acidification according to themethods disclosed herein.

FIG. 2 shows overall balanced equations for the reaction of metal bulkmaterials and HNO₃.

FIGS. 3A and 3B are optical microscope images of Al₁₃ (FIG. 3A) and Ga₁₃(FIG. 3B) single crystal produced from the acidification processdisclosed herein.

FIGS. 4A and 4B show dynamic light scattering of Al₁₃ (FIG. 4A) and Ga₁₃(FIG. 4B) in 0.1 M aqueous solutions.

FIGS. 5A and 5B are solid state Raman spectra of Al₁₃ (FIG. 5A) and Ga₁₃(FIG. 5B). Both spectra are consistent with previous reports of bothclusters.

FIG. 6 is a powder x-ray of Al₁₃ experimental compared with literaturereferences.

FIG. 7 is a ²⁷Al NMR spectra of Al13 Keggin ions from differentsynthetic methods.

FIG. 8 is a graph showing dielectric constants for Al₂O₃ thin-films fromprecursors disclosed herein with selected ratios of NO₃ ⁻:Al³⁺. TheKeggin ion (Ratio 0.5 NO₃ ⁻:1 Al³⁺) shows a higher dielectric constant,suggesting that the material makes more continuous (less porous)thin-films with a 350° C. anneal. The inset shows the test structure ofthe MIS device used for the CV measurement.

DETAILED DESCRIPTION

Methods such as vapor deposition are effective for producingatomically-uniform metal oxide thin films; however the process isexpensive, time consuming, and product yields are low. Although solutionprocessing of M₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅ (M=Al or Ga) clustersis potentially a viable alternative to traditional deposition methods,product variability, reaction conditions, and long reaction times aredeterrents for large-scale production. Advancements in the understandingof cluster reactivity have allowed chemists to develop more efficientand safer methods that utilize reducing agents such as zinc andelectrochemical titrations to produce the aforementioned clusters. Thesemethods however have significant drawbacks that include: longcrystallization periods, extensive purification requirements, productionof toxic byproducts, and the use of non-trivial and often expensiveelectrochemical apparatuses.

Disclosed herein is a facile and non-toxic synthesis of M₁₃ clusters.For convenience, “M₁₃ clusters” refers to [M₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄]_(a)[X]_(15a), wherein a is an integer of 1 to 4,[M₁₃O₄(OH)₂₄(H₂O)₁₂)]_(b)[X]_(7b), wherein b is an integer of 1 to 4, ora mixture thereof, wherein M is Al or Ga and X is a counterion derivedfrom a protic acid. In certain embodiments, a M₁₃ cluster isM₁₃(μ₁₃-OH)₆(μ₂-OH)₁₈ (H₂O)₂₄(NO₃)₁₅. [M₁₃(μ₃-OH)₆(μ2-OH)₁₈(H₂O)₂₄]_(a)[X]_(15a) is also known as “flat” M₁₃ and[M₁₃O₄(OH)₂₄(H₂O)₁₂)]_(b)[X]_(7b) is also known as “Keggin” M₁₃“Mnano-agglomerates” refers to a composition comprising M_(y) species,wherein y is 2 to 32. For example, M nano-agglomerates may include M₁₃clusters and at least one further M-containing component such as, forexample, M-containing dimers and/or trimers, and/or larger aggregatessuch as M₂₆, M₃₀, or M₃₂. This synthesis requires no purification andtakes advantage of acid-base chemistry to produce scalable quantities ofclusters, nano-agglomerates, and slurries in high quantitative yields.

In one embodiment, a simple, inexpensive, and atom economical method hasbeen developed to synthesize aqueous flat M₁₃ or Keggin M₁₃ nanoclustersvia acidification of representative mineral polymorphs of purifiedaluminum or gallium oxides, oxyhydroxides, and/or hydroxides (M₂O₃,MO(OH), or M(OH)₃ where M=Al or Ga).

Under this principle, the acidification can be done directly with themineral mined directly from the Earth, but would most likely requiresome form of purification and separation of other agglomerate materialthat may be present. With this synthetic route, these clusters can beproduced on a mass scale and be potentially utilized for solutionprocessing of amorphous metal oxide (M₂O₃) dielectric thin film devicescommercially. Additionally, the slurry mixture can be used as apolishing agent for surface smoothing.

Nanoscale clusters generally refers to discrete, monodispersedarchitectures of oligomers linked together with defined dimensions thatrange from 1 nm≤x nm<5 nm, while nano-agglomerate species refer todimensions ranging from 5 nm≤x nm<200 nm, and slurries are insolublemotifs that are 200 nm and beyond.

Aqueous nanoscale clusters, nano-agglomerates, and slurry mixtures havebeen synthesized via the acidification of bulk aluminum and galliumminerals/materials. This process can be carried out at wideconcentration gradients from, for example, 1 mM to 4 M metal content andrequires virtually no post-reaction purification or separation of excessmonomer formed or initial reactant material used. The acidificationproducts have a hydrodynamic radii of 1 nm±0.1 nm and can then be useddirectly “as is” as solution precursors for thin film fabrication solong as the original products used are pure (see, e.g., U.S. Pat. No.9,340,678, for a description of the use as precursors for thin filmfabrication). This synthetic route represents a facile, economical, andscalable scheme to mass-produce desirable precursor materials forsolution processing transparent thin film devices. Identification ofthese clusters in the solid and solution states with powder x-raydiffraction, optical microscopy, Raman spectroscopy, and dynamic lightscattering was consistent with data previously reported in theliterature.

More specifically, disclosed herein in certain embodiments are methodsfor reacting an aluminum containing polymorphs or a gallium containingpolymorphs with an acid to produce M₁₃ nanoscale clusters (e.g.,M₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅ nanoscale clusters). Also disclosedherein are methods of mixing an aluminum containing polymorph or agallium containing polymorph mineral with an acid to produce a slurry,and processing the slurry under high enough acidic conditions (metal toacid ratio >1:0.7 mol. eq.) sufficient to produce an aqueous solution ofM₁₃ nanoscale clusters (e.g., M₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅nanoscale clusters).

In principle, any representative mineral polymorph regardless ofoxidation state can be made into a slurry or solution nanoscale clusteror nanoagglomerate in solution under the following conditions: the finalproduct of cluster or agglomerate must contain a stabilizing protonaccepting ion [ex. NO₃ ⁻, PO₄ ³⁻, ClO₄ ⁻, SO₄ ²⁻, (X⁻ where X=F, Cl, Br,or I), CO₃ ²⁻, TsO⁻, MnO₄ ⁻, SeO₄ ²⁻] that would be generated via use oftheir corresponding acids, stable in the solid state and insoluble froma pH gradient of weakly acidic to weakly basic, and exhibitsamphoterism. Thus X in [M₁₃(μ₃-OH)₆(μ₂-OH)₁₈ (H₂O)₂₄]_(a)[X]_(15a) or[M₁₃O₄(OH)₂₄(H₂O)₁₂)]_(b)[X]_(7b) may be monovalent counterion (meaningthat subscript a orb is 1) or a polyvalent counterion (meaning thatsubscript a or b is greater than 1).

Illustrative aluminum-containing mineral polymorphs include corundum,gibbsite, boehmite, diaspore, bayerite, and nordstrandite and anycombination or mixture thereof. Illustrative gallium-containing mineralpolymorphs include Ga(O)OH, Ga₂O₃, Ga(OH)₃ (sohngeite), and anycombination or mixture thereof. The acid may be any acid that dissolvesthe mineral. Illustrative acids that have the ability to dissolve thematerial include nitric acid, sulfuric acid, selenic acid, halide acids(e.g., hydrochloric acid, hydrobromic acid, hydroiodic acid, chloricacid, bromic acid, iodic acid), sulfonic acids (e.g., tosylic acid,sulfanilic acid, benzene sulfonic acid, salicylic acid, Armstrong'sacid, triflic acid), carboxylic acids (formic acid, oxalic acid, aceticacid, carbonic acid), and a mixture thereof. Nitric acid is a preferredacid 1:0.3-1:0.65 mol. eq. of metal to acid ratio to produce slurriesand 1:0.7-1:1.15 mol eq. of metal to acid ratio to producenanoagglomerates, and 1:1.15-1:1.3 mol eq. of metal to acid to produceclusters). All other monovalent acids listed above will follow the samestoichiometry as nitric acid.

In certain embodiments, 1:1.15-1:1.3 mol eq. of metal to acid ratio willproduce flat [M₁₃(μ₃-OH)₆(μ₂-OH)₁₈ (H₂O)₂₄]_(a)[X]_(15a). Of note,[M₁₃(μ₃-OH)₆(μ₂-OH)₁₈ (H₂O)₂₄]_(a)[X]₁₅ clusters wherein X is polyvalentcounterion (e.g., a divalent counterion such as SO₄ ²⁻) can be producedby the methods disclosed herein.

In certain embodiments, 1:0.3-0.65 mol. eq. of metal to acid ratio (moreparticularly 1:0.45-0.65) will produce Keggin[M₁₃O₄(OH)₂₄(H₂O)₁₂)]_(b)[X]_(17b). Of note,[M₁₃O₄(OH)₂₄(H₂O)₁₂)]_(b)[X]_(7b) clusters wherein X is a monovalentcounterion (e.g., NO₃ ⁻) can be produced by the methods disclosedherein.

The mineral polymorph (M) is reacted with the acid, for example, at aM³⁺:NO₃ ⁻ molar ratio in a range to produce nanoscale clusters. Incertain embodiments, the M³⁺:NO₃ ⁻ molar ratio is tunable over a wideconcentration gradient, provided the M³⁺:NO₃ ⁻ molar ratio is controlledvia controlling the mol. eq. of metal to acid so that the reaction doesnot proceed to formation of the metal nitrate salt (e.g., Al(NO₃)₃ orgallium nitrate Ga(NO₃)₃). Overall balanced equations for the reactionof metal bulk materials and HNO₃ are shown in FIG. 1. The reactionparameters and overall balanced equations are also applicable to acidsother than nitric acid.

The mixing typically is carried out until complete dissolution occurs,causing a clear solution.

The slurry may be mixed at temperatures ranging from 25 to 100° C., moreparticularly 45 to 80° C., and most particularly 55 to 75° C.

The methods described herein may have a reaction time of 12 to 72 hours,more particularly 24 to 36 hours.

The methods disclosed herein do not require the use of any secondaryreagents to facilitate cluster formation (e.g., zinc powder or di-butylnitrosamine) or a potentially expensive electrochemical apparatus setup.

The methods disclosed herein can produce M₁₃ nanoscale clusters on amass scale since the methods are very amenable to scaling up. Forexample, different forms of aluminum and gallium minerals can be used asstarting materials under the same reaction conditions while consistentlyachieving the same M₁₃ end product. Only simple, inexpensive, andreadily available reagents are used and can be readily scaled up to atleast the kilogram scale. Atom economy for these methods is upwards of90% yield, with water being the primary byproduct.

The methods disclosed herein may result in the formation of an M₁₃nano-aggregate solution that has several different uses. For example,the M₁₃ nano-aggregate solution may be used as industrial polishingagent for chemical-mechanical planarization (CMP). In a further example,the M₁₃ nano-aggregate solution may be used as solution precursors forsolution processing of metal oxide (M₂O₃) thin films for electronicdevice. For instance, transparent conductive oxide materials containingAl³⁺ and/or Ga³⁺ species derived from the aqueous precursors disclosedherein may be made.

Certain illustrative embodiments are described in consecutively numberedclauses as shown below:

1. A method comprising:

reacting an aluminum mineral polymorph or a gallium mineral polymorphwith an acid at an aluminum metal to acid molar ratio or gallium metalto acid molar ratio sufficient to produceM₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅ nanoscale clusters,nano-agglomerates, or a slurry, wherein M is Al or Ga.

2. A method comprising:

mixing an aluminum mineral polymorph or a gallium mineral polymorph withan acid to produce a slurry; and

processing the slurry under conditions sufficient to produce an aqueoussolution of M₁₃(μ₃-OH)₆(μ₂-OH)₁₈ (H₂O)₂₄(NO₃)₁₅ nanoscale clusters,wherein M is Al or Ga.

3. The method of clause 1 or 2, wherein the aluminum mineral polymorphis selected from corundum, gibbsite, boehmite, diaspore, bayerite,nordstrandite, or any combination or mixture thereof.

4. The method of clause 1 or 2, wherein the gallium mineral polymorph isselected from Ga(O)OH, Ga₂O₃, Ga(OH)₃, or any combination or mixturethereof.

5. The method of any one of clauses 1 to 4, wherein the acid is selectedfrom nitric acid, sulfuric acid, selenic acid, a halide acid, a sulfonicacid, a carboxylic acid, or a mixture thereof.

6. The method of any of clauses 1 to 4, wherein the acid is nitric acid.

7. The method of any one of clauses 1 or 3 to 6, wherein the aluminummetal to acid molar ratio or gallium metal to acid molar ratio is 1:0.3mol eq of metal to acid to 1:1.3 mol. eq. of metal to acid.

8. The method of any of clauses 2 to 6, wherein the aluminum metal toacid molar ratio or gallium metal to acid molar ratio is greater than1:0.7 mol eq.

9. The method of clause 6, wherein the aluminum metal to acid molarratio or gallium metal to acid molar ratio is 1:0.3 to 1:0.65 mol eq toproduce the slurry.

10. The method of clause 6, wherein the aluminum metal to acid molarratio or gallium metal to acid molar ratio is 1:0.7 to 1:1.0 mol eq toproduce the nano-agglomerates.

11. The method of clause 6, wherein the aluminum metal to acid molarratio or gallium metal to acid molar ratio is 1:1.15 to 1:1.3 mol eq toproduce the nanoscale clusters.

12. The method of any one of clauses 1 to 11, wherein the method iscontrolled to avoid formation of Al(NO₃)₃ or Ga(NO₃)₃.

13. The method of any one of clauses 1 to 12, wherein the nanoscaleclusters have a dimension ranging from 1 nm to 5 nm.

14. The method of any one of clauses 1 or 3 to 12, wherein thenano-agglomerates have a dimension ranging from 5 nm to 200 nm.

15. The method of any one of clauses 1 or 3 to 12, wherein the slurrycomprises insoluble motifs having a dimension greater than 200 nm.

Examples Solution Preparation and Synthesis

All reagents were purchased from Sigma Aldrich and used without furthermodification. Varying M³⁺:NO₃ ⁻ molar ratios from 1:0.7-1.154 of M(OH)₃,MO(OH), or M₂O₃ powder to nitric acid (or other acids) are mixed underexternal ambient pressure forming slurry mixtures that range from 1 mMto 1 M metal content consistent throughout the reaction. The slurry ismagnetically stirred at 60° C. until clear, resulting in completesolution dissolution. No further modification to the solution is donefor solution phase spectroscopic measurements. For solid-statemeasurements aliquots of the solution were deposited on glass slides andallowed to crystallize for solid-state characterizations via Ramanspectroscopy and single x-ray crystallography.

Solid State and Solution Characterization

Prior to analysis, each sample was filtered into the cuvette with a 0.1PTFE, μm syringe filter to remove any particulate matter. The followingdynamic light scattering (DLS) and phase analysis light scattering(PALS) measured using the Mobiuζ from Wyatt technologies. DLS was usedto measure the hydrodynamic radius (R_(h)) of the alumina species insolution. The Dynamics software uses the Einstein-Stokes equation(R_(h)=K_(b)T/6πηD_(t)) where K_(b)=the Boltzmann constant, Ttemperature in kelvin, η=viscosity, and D_(t)=translational diffusioncoefficient to solve for the R_(h) value.

Raman spectra were collected using an Alpha 300S SNOM confocal Ramanmicroscope in a 180° backscattering configuration. A continuous wavepump laser provided ˜50 mW of power with an excitation wavelength of 53nm. A 0.3 m spectrometer equipped with 600 grooves/mm grating was usedto detect stokes Raman scattering and provided a resolution of 1 cm⁻¹.The spectra from each sample were averaged over 100 accumulations at 1second exposure times. The 520.5 cm⁻¹ peak of Si was used as an internalstandard.

FIG. 2 is a structural representation of various aluminum materials thatwere converted to flat-Al₁₃ clusters via acidification according to themethods disclosed herein.

FIGS. 3A and 3B are optical microscope images of Al₁₃ (FIG. 3A) and Ga₁₃(FIG. 3B) single crystal produced from the acidification processdisclosed herein.

FIGS. 4A and 4B show dynamic light scattering of Al₁₃ (FIG. 4A) and Ga₁₃(FIG. 4B) in 0.1 M aqueous solutions.

FIGS. 5A and 5B are solid state Raman spectra of Al₁₃ (FIG. 5A) and Ga₁₃(FIG. 5B). Both spectra are consistent with previous reports of bothclusters.

FIG. 6 is a powder x-ray of Al₁₃ experimental compared with literaturereferences.

Synthesis of Aluminum Al₁₃ Keggin Ion by Controlled Dissolution ofAl(OH)₃ in an Aqueous Monoprotic Acid

The aluminum Al₁₃ Keggin cluster [Al₁₃O₄(OH)₂₄(H₂O)₁₂)⁷⁺] is widely usedin applications such as water treatment and flocculation. The currentsynthetic procedure to produce the cluster is addition of an aqueousbase, e.g. NaOH, KOH, NH₃, or Ca(OH)₂ to an aqueous solution of Al(NO₃)₃or AlCl₃. By adding 0.54 parts of a monoprotic strong acid to 1 partAl(OH)₃ under mild heating conditions (60-90° C.), the Keggin ion formsin high yield. The product of this synthesis has been scaled to literquantities at concentrations as high as 1 M with respect to Al. Thisapproach yields a material free of alkali, alkaline-earth, andtransition-metal ions, leading to a protonated version of the materialfor water remediation and flocculation. FIG. 7 shows the NMR spectrum ofthe material synthesized using the traditional NaOH titration ofAl(NO₃)₃ compared to this claimed dissolution method. Clearly, thespectra from acid addition match the characteristic spectrum for theNa-Keggin [(NaAl₁₃O₄(OH)₂₄(H₂O)₁₂)⁷⁺].

Additional work shows that the Al₁₃ Keggin cluster[(Al₁₃O₄(OH)₂₄(H₂O)₁₂)⁷⁺] can be used as a precursor for solutionprocessed amorphous thin-film dielectric materials. Initial data from anMIS test structure suggests an improved quality of film properties usingalumina precursors with decreased counterion concentration afterannealing at 350° C. (FIG. 8).

In view of the many possible embodiments to which the principles of thedisclosed compositions and methods may be applied, it should berecognized that the illustrated embodiments are only preferred examplesof the invention and should not be taken as limiting the scope of theinvention.

What is claimed is:
 1. A method comprising: reacting an aluminum mineralpolymorph with an acid at an aluminum metal to acid molar ratiosufficient to produce M₁₃ nanoscale clusters, M nano-agglomerates, or aM₁₃ slurry, wherein M is Al and the aluminum metal to acid molar ratiois 1:0.3 mol eq of metal to acid to 1:1.3 mol. eq. of metal to acid. 2.The method of claim 1, wherein the aluminum mineral polymorph isselected from corundum, gibbsite, boehmite, diaspore, bayerite,nordstrandite, or any combination or mixture thereof.
 3. The method ofclaim 1, wherein the acid is selected from nitric acid, sulfuric acid,selenic acid, a halide acid, a sulfonic acid, a carboxylic acid, or amixture thereof.
 4. The method of claim 1, wherein the acid is nitricacid.
 5. The method of claim 1, wherein the aluminum metal to acid molarratio is greater than 1:0.7 mol eq.
 6. The method of claim 1, whereinthe aluminum metal to acid molar ratio is 1:0.3 to 1:0.65 mol eq toproduce the slurry.
 7. The method of claim 1, wherein the aluminum metalto acid molar is 1:0.7 to 1:1.0 mol eq to produce the nano-agglomerates.8. The method of claim 1, wherein the aluminum metal to acid molar ratiois 1:1.15 to 1:1.3 mol eq to produce the nanoscale clusters.
 9. Themethod of claim 1, wherein the method is controlled to avoid formationof Al(NO₃)₃.
 10. The method of claim 1, wherein the nanoscale clustershave a dimension ranging from 1 nm to 5 nm.
 11. The method of claim 1,wherein the nano-agglomerates have a dimension ranging from 5 nm to 200nm.
 12. The method of claim 5, wherein the acid is nitric acid.
 13. Themethod of claim 5, wherein the aluminum mineral polymorph is selectedfrom corundum, gibbsite, boehmite, diaspore, bayerite, nordstrandite, orany combination or mixture thereof.
 14. The method of claim 12, whereinthe aluminum mineral polymorph is selected from corundum, gibbsite,boehmite, diaspore, bayerite, nordstrandite, or any combination ormixture thereof.